The present invention relates generally to an injection-molding apparatus, and more particularly to an injection-molding apparatus for making ceramic moldings.
Ceramic moldings have been conventionally produced by various pressing operations. However, it is now also known from the prior art to produce them by injection molding using a molding apparatus having a stationary plate carrying one part of a mold and a movable plate having another part of the mold, so that the mold parts together form the mold cavity. The stationary mold part, that is the one on the stationary plate, has a bore through which the ceramic mass that is to be converted into a ceramic molding, is admitted into the mold cavity. After the material has been admitted into the mold cavity, a compacting pressure is exerted upon it and thereupon the mold is opened and the finished ceramic molding is removed.
As compared to the earlier approach to the manufacture of ceramic moldings, i.e., ceramic bodies, this latter prior-art proposal provides a significant advantage in terms of manufacturing speed. However, it also still suffers from certain disadvantages. One of these results from the fact that this latter prior-art proposal utilizes an injection cylinder to which the ceramic material is supplied in form of plugs on a conveyor, which plugs are then pushed into the cylinder by a piston before they can be injected from the cylinder and into the mold. This construction is of necessity very long and therefore requires significant space that is often at a premium. Moreover, free access to the arrangement is difficult because of the auxiliary components, such as the conveyor, and the feeding speed of the conveyor must be precisely coordinated with the reciprocating speed of the piston and with the opening and closing movements of the mold, since otherwise the apparatus will malfunction.
Moreover, the compacting pressure that is exerted in this prior art upon the material admitted into the mold cavity, is exerted by means of a pin which enters via an opening formed in the mold. It has been found that frequently some of the material will run back out of the mold cavity and foul the opening into which the pin exerting the compacting pressure must be able to enter. This causes operating difficulties.